IBR Approved · Stainless Steel
ASTM A403 WP321 Buttweld Pipe Fittings
Titanium-stabilised 321 (18Cr-10Ni-Ti) austenitic stainless steel — for high-temperature service to 815°C without sensitization. Exhaust systems, expansion joints and heat-exchanger headers. Elbows, tees, reducers and caps to ASME B16.9 / B16.28, IBR approved with Form III-C, EN 10204 3.1 / 3.2 traceable.
Grade Overview
ASTM / ASME A403 WP321 is a titanium-stabilised austenitic stainless steel. Titanium is added at a minimum of five times the carbon content to tie up carbon as stable titanium carbides, preventing chromium-carbide precipitation (sensitization) during prolonged exposure in the 425–815°C range. This makes 321 the standard choice for high-temperature components that cannot be solution annealed after welding.
321 fittings are supplied IBR approved with Form III-C for boiler and steam service. The EN counterpart is 1.4541 (X6CrNiTi18-10).
✓ No PWHT — welded with ER347 filler
As an austenitic stainless steel, 321 does not require post-weld heat treatment. It is welded with ER347 (niobium-stabilised) filler, not ER321, because titanium is lost across the welding arc — the niobium-stabilised filler provides equivalent weld-metal stabilisation. ASME P-No. 8, Group 1.
Chemical Composition — WP321 / 1.4541
| Standard | C | Cr | Ni | Ti | Mn | Si |
|---|---|---|---|---|---|---|
| ASTM A403 WP321 | ≤0.08 | 17.0–19.0 | 9.0–12.0 | 5×C – 0.70 | ≤2.0 | ≤1.0 |
| EN 1.4541 | ≤0.08 | 17.0–19.0 | 9.0–12.0 | 5×C – 0.70 | ≤2.0 | ≤1.0 |
Mechanical Properties — WP321
| Property | Requirement |
|---|---|
| Tensile Strength (min) | 515 MPa (75 ksi) |
| Yield Strength (min) | 205 MPa (30 ksi) |
| Elongation (min) | ≥ 35% |
| Heat Treatment | Solution annealed |
Equivalent Grades
| Product Form | Specification |
|---|---|
| Buttweld fittings | ASTM / ASME A403 WP321 · EN 1.4541 · UNS S32100 |
| Seamless pipe | ASTM A312 TP321 |
| Forgings / flanges | ASTM A182 F321 |
| Plate | ASTM A240 321 |
Fitting Types Available in 321
- Elbows — 45° / 90° / 180°, LR & SR
- Tees — equal & reducing
- Reducers — concentric & eccentric
- Caps & Stub Ends — closures & lap joints